Molded case circuit breakers include a single phased or multi-phased trip unit and a base, whereby the trip unit can be installed or removed from the base module. However, due to the number of components in the trip unit and the base as well as the space requirements of the circuit breaker, the amount of spacing between the trip unit and the base is extremely limited.
FIG. 1A illustrates a front view of an existing example molded case circuit breaker with a trip unit coupled to the base. As shown, the trip unit 10 includes three dielectric enclosures 11, each of which houses a current transformer (CT) 12 and represents a phase. The enclosures 11 are separated by dielectric walls 14 located in exterior spaces between the enclosures 11 of the trip unit 10. The base 20 in FIG. 1A includes a bottom surface 22 from which a pair of dielectric members 24 vertically extend upwards. When the trip unit 10 is secured to the base 20, the dielectric members 24 and the dielectric walls 14 are positioned to be vertically aligned with one another, as shown in FIG. 1A. However, as shown in FIG. 1A, a small horizontal space (represented by arrows 25) is present between the dielectric walls 14 and the dielectric members 24 when the trip unit 10 is secured to the base 20.
If the circuit breaker has interrupted an electrical fault, i.e. tripped, the trip unit 10 can be displaced from the base 20, by pressure build up of escaping arc gases between the unit 10 and the base 20, thereby causing debris from the interruption to travel along the vents 26 between the bottom surface 16 of the trip unit 10 and the bottom surface 22 of the base 20. As shown in FIG. 1B, as the trip unit 10 is displaced vertically away from the base 20, the horizontal spaces between the bottom of the dielectric walls 14 and the top of the dielectric members 24 increases. The escaping gases will cause a substantial amount debris to travel freely (as shown by the arrows) between the trip unit 10 and the base 20. This results in debris accumulating on the trip unit 10, the base 20 and areas between the two components. This accumulation of debris can eventually result in a breakdown in the dielectric path between the phases of the trip unit 10.
The present disclosure is directed to a molded case circuit breaker having a multi-phase trip unit and base that include interconnecting dielectric protrusions and dielectric members, respectively, that maintain a dielectric barrier between the different phases of the trip unit during a circuit breaker interrupt.